Piston head for internal combustion engines



Sept. 24, 1957 R. CRAMER, JR

PISTON HEAD FOR INTERNAL COMBUSTION ENGINES 5 SheetsSheet 1 Filed Aug. 3, 1955 J/Z'arneys p 1957 R. CRAMER, JR 2,807,247

PISTON HEAD FOR INTERNAL COMBUSTION ENGINES Filed Aug. 3, 1955 5 Sheets-Sheet 2 Sept. 24, 1957 R. CRAMER, JR

PISTON HEAD FOR INTERNAL COMBUSTION ENGINES Filed Aug. 3, 1955 5 Sheets-Sheet 3 9% luu hwa 0 E 5 2 2 WM 6 5 6 5 I II I7? yen for Z 5 206021 7077762177? Sept. 24, 1957 R. CRAMER, JR

PISTON HEAD FOR INTERNAL COMBUSTION ENGINES Filed Aug. :5, 1955 5 Sheets-Sheet 4 r? 6 i mw w; W r QQT \V w\ wm mm RM? .1. 3 9 hmp flay m w n X 1 1% H l\\ l\\\ ,w.

5 Sheets-Sheet 5 W 5 7 w a 5 Qj\ \NTL w {L1 -lllull l L I I 4 M y United States Patent PISTON HEAD FOR INTERNAL COMBUSTION ENGINES Robert Cramer, Jr., Hales Corners, Wis., assignor to Nordberg Manufacturing Company, Milwaukee, Wis, acorporation of Wisconsin Application August 3, 1955, Serial No. 526,123

' 12 Claims. or. 123-4138) This is a continuation-in-part of my prior application Serial No. 462,757, filed October 18, 1954, now abandoned.

This invention is in the field of pistons usable in internal combustion engines and constructed for this purpose although my new type of piston is not necessarily restricted to engine use. Y

A primary object of my invention is a new and improved piston head constructed to give longer service under severe operating conditions.

Another object is a piston head usable in internal combustion engines and constructed so that the points of maximum stress, due to thermal expansion and gas pressure, will not occur in the same general location.

Another object is a piston head of the above type constructed to give longer service, due to the separation of its thermal and gas loads.

Another object is a piston structure composed of a piston head and what I term a cooling nozzle so that the gas load on the piston will be transmitted to the piston support or trunk through the nozzle and not through the skirt of the piston head.

Another object is a piston structure in which the skirt of the piston head is free for thermal expansion.

Another object is a piston head with a new and improved cooling fluid circulation system.

Another object is a piston head with a cooling fluid system, as set forth above, and having a sealing structure arranged for a long life.

Another object is a piston head with a fluid system of the above type having a pressure dam to protect its fluid seal.

Another object is a removable and replaceable piston head structure composed of a piston head and a cooling nozzle which are each removable and together constitute a replaceable piston head unit or package.

Another object is a fluid cooled piston head structure adapted to be mounted on a piston trunk, wrist pin carrier, or other type of support.

Another object is a piston head structure in which a piston head with a skirt carrying a plurality of piston rings is mounted on a support and defines a continuous cylindrical fluid inlet passage with it which communicates inwardly with a fluid chamber under the crown of the piston head so that cooling fluid, when it is still relatively cool, will flow past the piston ring areas and then radially inwardly under the hot crown to a suitable outlet.

Another object is a piston head constructed sothat at the point of maximum stress, the cooling fluid in the piston head will be at its highest velocity, so that the rate of heat transfer will be at a maximum.

Other objects will appear from time to time in the ensuing specification and drawings in which:

Figure 1 is a longitudinal sectional view of a cylinder and piston with my invention;

Figure 2 is aview similar to Figure 1, but on an enlarged scale, and partly in section, taken generally at right angles to Figure 1;

Figure 3 is an enlarged sectional view of the piston head shown in Figure 1;

Figure 4 is a top view of the cooling nozzle shown in Figure 1;

Figure 5 is a sectional view taken along line 5-5 of Figure 4; p Figure 6 is a longitudinal sectional view, similar to Figure l, of a modified or variant form; and

Figure 7 is a section taken at right angles to Figure 6.

A conventional engine cylinder is shown in Figure l and is composed of the usual cylinder liner 10 with a cylinder head 12 defining a combustion chamber 14 with the top of the piston. The piston structure shown in the cylinder is composed of a piston trunk or support 16 having the usual wrist pin 18 and connecting rod 20. The lower end of the support is provided with the usual oil scraper rings or oil control rings 22 and the trunk has the usual ring sectors 24 disposed in a conventional manner.

A piston head structure, indicated generally at 26, is mounted on the top of the trunk or support and is composed primarily of what I term a cooling nozzle 28 and a piston head 30. The nozzle is connected to the top of the trunk support by a plurality of studs 32, as shown in Figure 2, with suitable nuts 34 which are accessible through the openings 35 in the side of the trunk. A plurality of positioning dowels 36 can project between. the nozzle and support to suitably position the nozzle.

The piston head mayhave the usual upper surface dished formation as at 38 with a cylindrical depending skirt 40 which surrounds the nozzle and carries a plurality of conventional piston rings 42. The nozzle. and skirt of the piston head are threaded together, as at 44, while the piston head is held against rotation by one or more dowels 46.

The cooling nozzle is shown in detail in Figures 4 and 5 and has an annular fluid channel 48 between an inner Wall 50 and an outer Wall 52. A plurality of openings 52' are provided in the wall to provide for core removal after the nozzle is cast, but these are closed by suitable plugs 53, in Figure 1, when the nozzle and piston head are assembled. A fluid connection 54 leads into the chamber and a plurality of radial passages 56 lead outwardly to an annular passage 58, in Figure 1, between the nozzle and piston head. The threaded connection 44 blocks the lower end of this passage and the fluid flows up and through a plurality of restricted passages disposed inwardly into a center chamber 60 between the crown of the piston and a top wall 62 on the cooling nozzle. The fluidr'then flows through a suitable opening 64 into the inner cavity 65 in the cooling-nozzle and downwardly through appropriate openings in the piston trunk leading to a chamber 66 which is connected by a passage 67 to a fluid discharge pipe 68 that leads to the fluid supply sump in the conventional manner.

The top of the cooling nozzle is provided with a plurality of radial slots 69 which divide an annular bearing surface 70 into segments. These segments oppose acorresponding annular ring 71 formed on the lower face 72 of the crown of the piston head. Thus the radial slotse69 in the top. of the cooling nozzle define a plurality of thin passages to allow the fluid to flow rapidly to the center chamber and then to the discharge. The passage 58, between the skirt and the cooling nozzle, is also thin and the fluid flows very rapidly up to the slots 69.

An O-ring seal 73 is provided below the threaded connection 44 to prevent the cooling fluid from getting into the cylinder and at the same time to prevent the gases from the combustion chamber from getting into the cooling system.

The cooling fluid issupplied to the nozzle through the usual channel 74 in the connecting rod, an axial passage 76 in the wrist pin and a connecting pipe 78 leading to the opening 54 in the nozzle.

In Figures 6 and 7, I have shown a variant form in which the piston rod is connected to a wrist pin carrier 77 by a wrist pin having a central channel 78 for lubricating and'cooling fluid. The carrier has a correspond ing channel 79 to allow the fluid to flow into a central chamber 80 in a cooling nozzle 81. This nozzle may be connected to the top of the wrist pin carrier by a suitable number of bolts 82, and a plurality of radially disposed outlet passages 83 are provided through the sides of the nozzle to allow the fluid to flow out.

A piston head 84 is mounted on the nozzle and has a depending skirt 85 which extends below the wrist pin carrier and is held in place by a snap ring 86 which bears against the lower surface of the wrist pin carrier. The nozzle and piston head define a thin section annular chamber 87 between them which receives fluid through the radial passages 83, and a disc-shaped chamber 88 exists between the crown of the piston head and 'the upper surface of the nozzle. The lower end of the chamber 87 may be closed by a suitable seal 87'. The crown and cooling nozzle are provided with annular bearing surfaces, as in the previous form, and radial slots are formed in the bearing surface on the cooling nozzle so that fluid can flow upwardly in the chamber 87 and radially inward into the central chamber 88. A suitable discharge 89 is provided in the center of the chamber leading ofl to one side and the fluid is allowed to empty into the crank case by suitable discharge passages 91 in the wrist pin carrier and an outlet 92 in an oil control ring carrier 93 bolted to the lower end of the wrist pin carrier by any suitable number of bolts 94 or the like. Clearance can be provided at 95 between the end of the skirt and the control ring carrier so that the skirt of the piston head can expand and contract.

The use, operation and function of my invention are as follows:

The total load imposed on an engine piston is made up actually of two loads or stresses, one being the expansion of the metal in the piston head due to the high temperature developed in the cylinder, called the thermal load, and the other being of the compressive force bearing down on the piston head caused by the high pressure developed in the cylinder, this latter being referred to as the gas load. These two loads combine to impose a maximum stress approximately at the point 100 in Figures 1 and 6 so that in a conventional engine, piston failures generally occur in the form of cracks across the piston wall at this point.

By my invention, the thermal and gas loads are separated so that they do not pass through the same point.

The thermal expansion of the crown will cause a tensile stress at the point 100; however, this is greatly reduced as the lower end of the skirt of the piston is free to expand because the threaded connection 44 in Figure 1 has suflicient clearance and is sufliciently loose for this purpose. A slight clearance exists, as at 101 in Figure 1, between the lower end of the head and the top of the piston trunk or support. Clearance may also exist at 91 between the end of the skirt and the scraper ring carrier. carried through the crown of the piston head to the cooling nozzle through the abutting annular surfaces. The skirt of the piston head does not carry'any of the gas load, and it is free to expand and contract under the thermal load. V

The gas load will be directed downwardly through the crown, as indicated by the arrow 102 on to the cooling nozzle and then into the piston trunk, support, or wrist pin carrier, and this is done without the use It should be noted that the gas loadwill be away from the point 100. The wall or walls of the cooling nozzle carries the gas load to the wrist pin carrier or support. Therefore, the usual cyclical gas load will no longer be imposed on the piston at the point and this results in a much longer life for the piston. Also the bending stress on the crown will be that of a much smaller diameter piston, equivalent to the diameter of the bearing surface 71 in Figure 1. The same is true of Figure 6.

In the Figure 1 form, the O-ring 73 prevents the cooling fluid from getting into the cylinder. O-rings are well known as excellent static seals; however, their life is limited if they are exposed to severe pressure fluctuations. The O-ring 73 has been placed on the other side of the threaded connection 44 from the cooling fluid chamber 58 so that it is protected from the cooling fluid pressure fluctuation set up by the inertia forces in the rapidly reciprocating piston. The threaded section, in a sense, acts as a damper or dam and reduces the magnitude of the pressure fluctuations on the O-ring. Thus the life of this seal will be greatly increased.

It should be noted in the Figure 1 form that the threaded section serves a double function: first, it connects the piston head and cooling nozzle, and second, it dampens the fluid pressure fluctuations against the O-ring. The thread is made with large clearance, and its direction of tightening is such that expansion tends to loosen the thread; thus the gas load at all times is transmitted through 102 and not through the thread.

The fluid chamber in the cooling nozzle with its radial distribution holes is arranged to secure generally equal distribution of the cooling fluid. The annular passage 58 in Figure l and 87 in Figure 6 is very thin to secure high velocity of fluid flow, particularly behind the piston rings and its upper part where the cooling fluid flows past the stress point 100. The radial slots 69 are thin, so that the fluid will have a maximum velocity along this part of its travel. Thus the heat transfer rate from the surrounding wall surfaces will be maximum in the annular passage and slots 69, due to the high velocity of the fluid. It should be noted that it is normally these two sections (as the fluid moves up behind the rings and turns in toward the center chamber 60 in Figure 1 and 88 in Figure 6), that require the cooling. Therefore, by this structure the heat in this critical area will be carried away by the fluid at a maximum rate.

It should be noted that the piston head and cooling nozzle are, in a sense, a package and can be attached to a conventional piston trunk or wrist pin carrier as a substitute or replacement for a piston head of conventional design. The invention, therefore, has increased utility, due to its feasibility as a repair part package. At the same time it can, of course, be used upon any original installation. i i

In the Figure 6 form, the piston head is merely held on .by the snap ring in the skirt, and it is free to expand and contract both laterally and'longitudinally; I have shown a web type internal structure 93 in the cooling nozzle, but this is not absolutely necessary, as the cooling nozzle could be built with an inner wall, as in Figure 1. Also, the crown of the piston head has been shown as slightly convex, but it could be dished out or concave, as in Figure l. The details of the fluid supply and return passagesin both forms of the invention arenot important, and I have not shown or described them except briefly.

It will be realized that whereas I have described and illustrated a practical and operative device and one modification, nevertheless, many changes may be made in the size, shape, arrangement, number and disposition of parts without departing materially from the spirit of my invention. For example, the piston head could be convex, concave, or flat. Also the slots 69 could be in the ring 71 on the inside of the piston head. While I have shown a particular form of trunk structure and wrist pin carrier, any suitable piston head support will do. I have not shown any fuel supply device, but it should be understood that a conventional fuel injector, gas valve, carburetor, or otherwise, could be used. The radial holes 83 in Figure 6 might be radial slots in the bottom of the nozzle. I wish, therefore, that my showing be taken as in a large sense illustrative or diagrammatic rather than as limiting me to my precise illustration.

I claim:

1. In a piston head assembly, a main support, a piston head on the support having a crown and a depending skirt, annular bearing surfaces between the top of the support and the inner surface of the crown to transmit the gas load from the crown of the piston to the support, and means for securing the piston head on the support so that the crown may expand and contract freely in a lateral direction and the skirt may expand and contract freely in a longitudinal direction under the thermal load.

2. The structure of claim 1 in which the piston head is constructed and arranged to be free to rotate on the support.

3. The structure of claim 1 in which the piston head and the support are screwed together.

4. For use with a piston, an internal cooling support adapted to be mounted on the top of a piston support, a piston head adapted to be mounted on the internal cooling support and having a depending skirt which surrounds it, the lower inside surface of the piston head bearing against the top of the internal cooling support to transmit the compressive loads to the cooling support, opposed annular bearing surfaces of relatively large diameter between the crown and internal cooling support so that the cooling support transmits the compressive load to the piston support, the depending skirt of the piston head being relatively free to expand and contract under thermal loads and carrying no compressive loads, means for connecting the piston head to one of the supports, and radial passages through the bearing surfaces between the lower inner surface of the piston head and the cooling support for circulation of a cooling fluid.

5. The structure of claim 4 in which the cooling support is connected to the skirt by a threaded section.

6. The structure of claim 5 characterized by and including an O-ring seal between the skirt and cooling support below the threaded section.

7. For use in a piston assembly, a piston head having a crown and a depending skirt, a large diameter annular bearing surface on the lower surface of the crown relatively adjacent the junction between the crown and skirt adapted to bear against a support to transmit the gas load from the piston head to the support, and means on the inner surface of the skirt for connecting the piston head to the support so that the skirt can expand and contract longitudinally and the crown can expand laterally under the thermal load on the piston head.

8. The structure of claim 7 further characterized in that said last mentioned means includes a threaded section.

9. The structure of claim 7 further characterized in that said last mentioned means includes a continuous slot adapted to accept a snap ring.

10. For use in a piston assembly for an internal combustion engine, an internal cooling support constructed to be mounted on a piston support and including an inverted cup-shaped body with an upper annular bearing surface for engagement with a piston head to transmit the gas load to the piston support, the diameter of the bearing surface being only slightly less than the outside diameter of the cooling nozzle, and a generally cylindrical depending frame having a cooling fluid chamber adapted to be connected to a fluid inlet, a plurality of radial passages opening outwardly from the chamber through the frame, a plurality of spaced radial slots through the annular bearing surface, and means for connecting the cooling support to the piston support.

11. The structure of claim 10 further characterized by and including a threaded section on the outside of the generally cylindrical depending frame below the plurality of radial passages that open outwardly from the chamber.

12. The structure of claim 10 further characterized in that the cooling fluid chamber includes a generally open central reservoir occupying substantially the entire central portion of the cooling support.

References Cited in the file of this patent UNITED STATES PATENTS 1,547,687 Rohwer July 28, 1925 2,266,192 Grieshaber Dec. 16, 1941 2,304,891 Dickson Dec. 15, 1942 FOREIGN PATENTS 487,377 Great Britain June 20, 1938 883,310 France Mar. 22, 1943 856,535 Germany Nov. 24, 1952 

